1. Field of the Invention
This invention relates to the field of mining and excavation equipment. More specifically, the invention comprises an improved rigging system for dragline buckets that reduces the need for heavy chains.
2. Description of the Related Art
In order to understand the significance of the present invention, it is important to have some understanding of conventional dragline bucket rigging. FIG. 1 shows dragline bucket assembly 10. As those skilled in the art will know, the dragline bucket assembly is lifted and positioned by a boom crane—typically a very large boom crane. Bucket 24 is nearly always made of thick steel. The width of the bucket's mouth may be as much as twenty feet (6 meters). The bucket itself often weighs many tons.
In operation, the bucket is swung into position and then dropped into the material that is to be removed. The mouth of the bucket is typically given a downward pitch during the drop operation so that it digs into the material. The bucket is then dragged back toward the boom crane. As it is dragged along the bucket's mouth scoops in a load of material. FIG. 1 shows the configuration of the dragline bucket assembly during a typical scooping phase.
Once the bucket is full the boom crane is used to pull the bucket assembly free of the material. The boom crane then swings the bucket toward the area where the scooped material is to be deposited. When the bucket assembly reaches the deposit area, a dumping mechanism causes the bucket to pitch downward. The contents of the bucket then spill from the bucket's mouth. Once the bucket is empty, the cycle repeats.
Bucket 24 and its contents are primarily suspended by a pair of lift trunnion assemblies 22—with a trunnion assembly being located on each side of the bucket. A lower hoist chain 20 connects each trunnion to spreader bar 18. An upper hoist chain 16 connects each side of the spreader bar to yoke 48.
The term “yoke” refers to the component that connects the upper hoist chains to the tensile members used to lift the entire bucket assembly. It is also typically used to connect the chains to the dump block assembly. It can take on many shapes and forms. In the example of FIG. 1, yoke 48 connects upper hoist chains 16 to a pair of lift ropes 14 (Each lift rope 14 is connected to a socket 12). In this context the term “rope” refers to any suitably flexible tensile member. A cable made of wrapped steel wires is often used as a lift rope.
The yoke may be a single large casting or it may be an assembly of several pieces. The term should be broadly construed to mean anything that connects the bucket assembly rigging to the lifting cables leading to the boom on the crane.
As stated previously, the lift ropes connect the bucket assembly to the boom of the crane. Yoke 48 also provides an attachment point for dump block 28. As the name suggests, a mechanism incorporating the dump block is used to change the bucket from its scooping configuration to its dumping configuration. When this mechanism is actuated, the bucket pivots downward about the two trunnion assemblies. The mouth of the bucket pitches downward and the tail of the bucket rises. Once the bucket's contents are completely dumped, the dumping mechanism is reversed and the bucket is returned to its digging orientation.
Still referring to FIG. 1, one or more drag lines 36 are attached to the rigging shown via drag socket 34. A drag line(s) is used to pull the bucket toward the crane once the bucket has been dropped into the material. A drag line is also commonly used to regulate the bucket's orientation. Drag chains 30 connect drag socket 34 to the sides of the bucket. The drag chains attach to bucket 24 on either side of the bucket's mouth. Arch 32 is typically provided to reinforce the bucket's open mouth.
The reader will note that a dump rope 26 passes from the drag socket 34, around dump block 28 and connects to the upper portion of arch 32. The dump rope is used to regulate the transition of the bucket between its digging and dumping orientations.
FIG. 2 shows the same assembly from a different vantage point. The reader will note that each drag chain is attached to the bucket using a large and robust drag chain hitch 40. The lifting chains may be divided into two categories: Lower hoist assembly 44 includes the two lifting chains connecting the trunnions to the spreader bar. The spreader bar itself may also be considered part of the lower hoist assembly. Upper hoist assembly 42 includes the lifting chains used to connect the spreader bar to the yoke. Top rail 38 extends around the top of the open bucket.
The bucket assembly is operated in a brutal environment. The bucket is typically dropped into an ore deposit containing rocks and other abrasive materials. Chains have traditionally been used near the bucket itself because of the extreme forces applied and the abrasive action of the material being dug. The chains shown in the assembly may be comparable in size to the termination chains used on a large ship. For example, each link may be well in excess of 1 foot (30+ centimeters) long.
Such chains are quite heavy. They must be serviced and replaced quite often as well. The size and weight of the chains make them difficult and dangerous to handle. In addition, the chains rapidly elongate while in use—primarily because of link-to-link abrasion. This elongation alters the dumping geometry of the bucket assembly and reduces its performance. In addition, the elongation of the lifting chains reduces the maximum height to which the bucket assembly may be lifted. The reduction in lift height reduces the amount of material that the dragline assembly can move. It would be advantageous to replace the chains with a lighter and less cumbersome material. It would also be advantageous to replace the chains with a tensile member that does not elongate significantly.
FIG. 3 shows a proposed replacement of the chains used in the upper hoist assembly. A pair of flexible tensile members 46 have been substituted for the chains used in the prior art. Chains are still used in the lower hoist assembly—since these components are subjected to the dropping and dragging operations of the bucket itself. It is likely that only a chain can be used in the lower hoist assembly as no other component is able to survive that environment, though it may ultimately be possible to use the present invention for the lower hoist components as well.
The reader will note that the cables used are free of the actual dropping and dragging operations—being above spreader bar 18. FIG. 5 shows a section view through the assembly that illustrates the position of the tensile members 46 compared to lower hoist assembly 44. Spreader bar 18 is needed to prevent the lower chains dragging along the side of the bucket and binding the dumping operations. However, above the rigid spreader bar, a more flexible tensile member may be used and one might therefore assume that the assembly of FIG. 3 provides a workable solution. Another problem exists, however.
A dragline bucket assembly must be periodically laid on the ground for servicing, shift changes, or other reasons. When the bucket assembly is placed on the ground and the boom is lowered, the lifting rigging falls over the bucket in random and unpredictable ways. FIG. 4 provides a detailed view of the upper and lower hoist assemblies when the bucket has been placed on the ground.
Tensile member 46 is flexible enough to lay across top rail 38 as shown. Spreader bar 18 and dump block 28 have both fallen on top of tensile member 46 and “pinched” it against top rail 38. Tensile member 46 may also be dragged along top rail 38 while being subjected to other forces. The spreader bar may weigh several tons and even the dump block assembly may exceed one ton in weight. Thus, the reader will perceive that even though tensile member 46 lies above the dropping and digging operations it is still subjected to extreme battering, bending, cutting, and compression forces when the bucket is laid down. Further, the orientation of the “pile” of heavy components created when the bucket is laid down is random and impossible to consistently predict.
Thus, even though it is possible to use a flexible tensile member in the upper hoist assembly, a conventional flexible tensile member is not likely to survive the full range of bucket operations. Some flexible designs have been evaluated over the years but no such design has ever been able to successfully compete with chain.
The advantages of using such a tensile member are promising, however. Any reduction in the weight of the bucket rigging means that a larger bucket can be used (for a given crane lifting capacity) and more fill material can be carried with each scoop. Any reduction in the stretching tendency of the tensile members used means that the assembly produces a more consistent bucket fill and soil mound height, thus increasing productivity. Any reduction in metal-to-metal wear increases the lifespan of a component and reduces the frequency of component replacement. Any reduction in the use of chain reduces the safety hazards inherent in the use of chain. Thus, a new type of flexible tensile member assembly that is able to withstand all the dragline bucket operations would be advantageous. A new type of flexible tensile member assembly that is able to employ modem synthetic materials would further reduce the weight of the rigging and provide an even greater advantage.